1. Field of the Invention
The present invention relates generally to the field of thermal writing of high density data media, and more particularly to the specific composition and methods of forming high density data recording products.
2. Description of the Related Art
Phase-change media are a widely available means for providing high density data storage, and such media may include CD-RW, DVD-RAM, and DVD-RW formats, among others. In this type of media, data is stored at a particular location, typically micron sized, and storage and erasure occurs based on the microstructure of the target region. FIG. 1 illustrates an ultra-high-density data storage device disclosed in U.S. Pat. No. 5,557,596 to Gibson et al. (the '596 patent). The ultra-high-density data storage device includes a set of field emitters 100, a data storage layer 110 that is located below the field emitters 100, a micromover 120 that holds the data storage layer 110 below the field emitters 100 and that can position the data storage layer 110 at desired locations relative to the field emitters 100, and electrical connections 130 that can supply energy to the field emitters 100. When supplied with energy, the field emitters 100 can bombard the data storage layer 110 with electron beams and can transform nanometer-scaled portions of the data storage layer from unwritten data bits, designated in FIG. 1 by the reference numeral 140, to written data bits, designated by the reference numeral 150. This transformation occurs via a writing process, discussed below.
When writing data to the data storage layer 110, respective field emitters 100 are energized through the electrical connections 130 and bombard the selected unwritten data bits 140 with electron beams. During the writing process, the electron beams are of sufficient power density to transform the bombarded unwritten data bits 140 from a first material state (e.g. a crystalline state, which may be assigned a “0” value) to a second material state (e.g. an amorphous state, which may be assigned a “1” value). Hence, a data bit having a value of “1” can be written to and stored on the data storage layer 110 by bombarding a crystalline, unwritten data bit 140 and by appropriately cooling (quenching) the data bit 140 to form an amorphous, written data bit 150, respectively.
When erasing data from the data storage layer 110, respective field emitters 100 are energized, through the electrical connections 130, and are made to bombard the selected written data bits 150 with electron beams. During the erasing process, the electron beams are of sufficient power density to transform the bombarded written data bits 150 from a second material state (e.g., an amorphous state, which may be assigned a “1” value) to a first material state (e.g., a crystalline state, which may be assigned a “0” value). Hence, a data bit having a value of “0” can be restored on the data storage layer 110 by bombarding an amorphous, written data bit 150, thereby appropriately heating (annealing) the data bit 150 to form a crystalline, erased data bit 140.
When reading data from the storage layer 110, the field emitters 100 again bombard the data bits 140, 150 with electron beams. However, instead of bombarding the data bits 140, 150 with electron beams that have sufficient energy to transform the data bits 140, 150 between the first and second material states discussed above, the field emitters 100 bombard the data bits 140, 150 with relatively low-power-density electron beams that do not effectuate a transformation but that do effectuate identification. Then, the interactions between the low-power-density electron beams and the data bits 140, 150 are monitored in order to read data.
During the reading operation, the low-power-density beams interact differently with unwritten data bits 140 than with written data bits 150. For example, a low-power-density beam may generate fewer secondary electrons when bombarding a crystalline, unwritten data bit 140 than when bombarding an amorphous, written data bit 150. Therefore, by monitoring the interactions between the relatively low-power-density beam and the data bit 140, 150 that the beam is bombarding (e.g. by monitoring the number of secondary electrons generated), it becomes possible to determine whether the bombarded data bit 140, 150 is storing a “1” or a “0” value and to read data stored in the data storage layer 110.
Certain implementations of the foregoing design have used a luminescent material on top of the phase-change material which, in turn, was above a photodetector. The various states of the of the phase-change layer, in both a written configuration and unwritten configuration, have different absorption and/or reflection coefficients for light given off by the luminescent material. Data may be read back using a low power density electron or optical beam to stimulate luminescence in the luminescent layer. Depending on the state of the phase-change layer below the area of the luminescent layer being stimulated, more or less light passes through the phase-change layer to the photodetector. The state of the phase-change layer in the region being addressed, either more or less absorptive and/or more or less reflective, may be assessed by monitoring light reaching the photodetector.
The problem with this light monitoring approach is that the luminescent layer must be manufactured on top of the phase-change layer, where “on top” refers to placing a layer further away from the base layer, or outward from the base layer of the medium. Placing a luminescent layer on top of the phase-change layer can require processing temperatures and conditions harmful to the phase-change layer. Further, during the write process, the luminescent layer must in certain cases withstand temperature changes higher than those required to affect the phase-change in the phase-change layer. The luminescent layer must also withstand bombardment by high energy electrons in some circumstances. High temperatures and/or bombardment by high energy electrons can adversely affect the luminescent properties of the luminescent layer.
Another potential disadvantage of this scheme is that the photodetector is below the phase-change layer, which can make manufacturing more difficult. Other problems may arise if too much light is absorbed or reflected in unwritten portions of the phase-change layer below a written bit intended to be transmissive, or if too much light internally reflects at the bottom surface of the phase-change layer. Also, in certain designs, significant light may be lost through the top surface of the luminescent layer rather than reflected down toward the phase-change layer where it can add to the signal. In certain other designs, a protective top layer may be needed over the luminescent layer to prevent unwanted changes or degradation during the reading and writing processes.
It would be advantageous to provide media having a phase-change-layer in combination with a luminescent material and detector that enables thermal writing and erasure of said media in a relatively efficient manner and avoids the problems associated with previous designs.